Friction reducing coatings for photographic elements



United States Patent Ofilice 3,295,979 Patented Jan. 3, 1967 This invention relates to photographic elements, and more particularly to friction reducing exterior backing layers for photographic elements.

Seusitized photographic elements, such as those having one or more gelatin silver halide emulsion coatings on a support, which may be composed of plastic film base, paper or coated paper, are inherently stiff and thus offer sufficient resistance to bending to cause serious problems in certain applications. For example, in some diffusion transfer processes the sensitized photographic element after exposure is drawn around an arcuate guide member into contact with a receiving sheet. The arcuate guide member is usually of such configuration that the photographic element must be bent at a sharp radius to pass thereover. In such photographic elements, it would be highly desirable to provide the back (unsensitized) side of the support with an exterior backing layer having good slipperiness to reduce friction between the support and the arcuate guide member to facilitate pulling the photographic element around the guide, and also to reduce chances of tearing the photographic element during this operation. Such backing layers would also facilitate movement of one photographic element across an adjacent photographic element.

Considerable difiiculties are involved in providing a satisfactory friction reducing layer. When many surfactants are incorporated in various hinders, the resultant coating becomes tacky and blocking rather than slippery. A further problem is that in some instances it is desirable to coat the back side of the support with a moisture impervious layer. It is very difficult to provide photographic elements with suitable moisture resistant coatings thereon which provide the desired friction-reducing function. Perhaps an even more stringent limitation on such coatings or layers is that they must not have any deleterious effects on the sensitized side of the photographic elements since such photographic elements are commonly cut in sheets and stacked so that any frictionreducing layer on the back of the support contacts the sensitized side of the adjacent photographic element.

One object of our invention is to provide frictionreducing exterior backing layers for photographic elements. Another object of our invention is to provide photographic elements having friction-reducing exterior backing layers, which photographic elements may be ea ily drawn across adjacent photographic elements and around arcuate guide members. A further object of our invention is to provide photographic supports having frictionreducing exterior backing layers. A still further object of our invention is to provide photographic elements having friction-reducing exterior backing layers, which photographic elements may be stacked upon one another without damage to the sensitized material on the photographic element by the backing coating of the adjacent photographic element. A still further object of our invention i to provide friction-reducing exterior backing layers for photographic elements, which layers are moisture resistant. Other objects of our invention will appear herein.

These and other objects of our invention are accomplished by providing photographic elements with an exterior backing layer comprising casein and about 110%, based on the dry weight of the casein, of an N-alkylaminopropionate, and/or N-alkyl-B-iminodipropionate salt.

We have found that exterior backing layers in accordance with our invention effectively reduce friction. These backing layers are photographically inert, and enable photographic elements having a light sensitive material on one side and an exterior backing layer in accordance with the invention on the other side, to be stacked on top of one another without deleterious effect to the light sensitive material by such backing layers. The backing layers of the invention are not blocking and are resistant to moisture.

Our invention will be further illustrated in the following examples.

EXAMPLE I A 17 lb./ 1000 sq. ft. photographic paper was coated on the wire side with two opaque plastic layer over which was applied a layer from an aqueous solution adjusted to pH 8.0 with ammonia, of casein, N-alkyl-B-iminodipropionate, sodium salt (alkyl ranging from 12 to 18 carbon atoms), dihydroxydioxane and chromic chloride at a coverage of about 4 grams casein per square meter. The layer contained about 5% N-alkyl-B-iminodipropionate, 2% dihydroxydioxane and 2% chromic chloride, all based on the weight of the dry casein. The face side of the paper was then coated with a low density polyethylene containing a white pigment at the rateof 3 lb./1000 sq. ft. The polyethylene coating was subjected to electrical corona discharge in the manner described in Alsup and Venor, US. patent application Serial No. 191,711, filed May 2, 1962. A panchromatically sensitized gelatin silver halide emulsion was then coated over the polyethylene coating of the paper support. The photographic element obtained was cut into sheets which were stacked With the backing layer of the invention contacting the emulsion side of the adjacent sheet without deleterious effect to the emulsion. The coefficients of friction of the photographic elements against the emulsion layer and against a polished stainless steel surface were measured and compared with similar photographic elements having (1) no backing layer and (2) a backing layer of casein alone in an IBM Paper Friction Tester sold by Abbot Axtell Inc., of Binghamton, New York, described in TAPPI, vol. 40, No. 12, Dec. 1957, p. 972, except that the weight employed was grams, rather than 1000 Hence, the backing layer of the invention provides a substantial reduction in friction in contact with the emulsion side of another photographic element or a polished metal surface.

EXAMPLE II A dyed opaque cellulose ester film support was coated with an aqueous solution containing casein, N-alkyl-,8- iminodipropionate, sodium salt (alkyl ranging from 12 to 18 carbon atoms), dihydroxydioxane and polymethylmethacrylate beads. The pH of the solution was adjusted =3 to about 8.0 with ammonia. The solution was coated as a layer onto film support at the following coverages:

Mg./sq. ft. Casein 284 N-alkyl-fi-iminodipropionate l 5 Dihydroxydioxane 22 Polyrnethylmethacrylate 25 The opposite side of the support was coated with a series of layers containing dye developers and silver halide emulsion layers as described in Example I, and as illustrated in FIG. 1, of Belgian Patent 607,420. Sheets of photographic elements obtained were stacked with the backing layer contacting the emulsion layer of the adjacent sheet without damage to the emulsion layer thereon. The reduction in friction was essentially the same as in Example I.

As indicated in the foregoing examples, the coating compositions of our invention may be conveniently applied from aqueous solutions having relatively high pH, such as about 8.0. The high pH allows good solutions of the casein. Preferably, the pH of the solution is adjusted with ammonia which evaporates from the coating to give a moisture resistant backing layer.

The thickness of the friction-reducing layers of our invention may be varied as desired over a relatively Wide range. These coatings may advantageously contain from .07 to .35 gram, preferably .25 to .30 gram, of casein per square foot of support. These layers may contain llO%, and preferably 4.5 to 5.5%, N-alkyl-B-aminopropionate or N-alkyl-fl-iminodipropionate, which have the following structural formula:

wherein R is an aliphatic hydrocarbon group containing -18 carbon atoms, R is H, an aliphatic hydrocarbon group of 10-18 carbon atoms or CH CH COOM, and M is H or a salt-forming substituent such as an alkali metal, e.g., sodium, potassium or the like, or ammonium. Preferably, R and R when R is alkyl, are aliphatic hydrocarbon groups of 12-18 carbon atoms. N-alkyl-fi-iminodipropionate, alkali metal salt, wherein the alkyl group contains 12-18 carbon atoms, provides highly satisfactory results.

We have found that hardeners such as dihydroxydioxane, formaldehyde, diacetal or chromic chloride, or the like, or matting agents (which also serves to reduce friction) such as polymethylmethacrylate beads, silica, starch or glass particles, or both are often advantageously incorporated in the coatings of the invention. The quantity of these constituents in the compositions may be varied over a relatively wide range to obtain the desired results. We have found that amounts of hardener and matting agent of from 1-3% each, based on the dry weight of the casein, produce highly satisfactory results.

As previously indicated, the coatings of our invention may advantageously be applied as an exterior back layer for photographic supports composed of paper, paper coated with various compositions including polyethylene, or film base such as cellulose acetate, cellulose acetate butyrate, polystyrene, polycarbonate or a polyester film base such as polyethylene terephthalate.

The supports coated in accordance with our invention may be used in the usual manner. Highly advantageous applications are in photographic elements which must be drawn around an arcuate guide and over the photosensitive material of various photographic elements, with the exterior back layer adjacent the arcuate guide. Such instances include photographic elements comprising a support carrying a photosensitive material on the face side, and a leader attached to the support which may be employed to pull the photographic element across an adjacent photographic element and around the arcuate 4 guide. Such photographic elements are illustrated in FIGS. 3 and 4 of US. Patent 2,946,270. These photographic elements are particularly useful in cameras of the type described in US. Patents 2,495,111 and 2,946,270.

The friction reducing coatings of our invention may also be advantageously applied to the back of receiving sheets, such as those comprising a support having on the face side a colloidal dispersion of physical development nuclei. Such elements may be drawn across adjacent photographic elements and around an arcuate guide with much greater ease than similar elements which do not possess the friction-reducing exterior back layer of the invention.

We have also found that the friction encountered in pulling one photographic element across an adjacent photographic element may be reduced by incorporatingN- alkyl-B-aminopropionate or N-alkyl-fi-iminodipropionate in the exterior layer, such as a protective gelatin layer, on the light sensitive side of the photographic element.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic support having on one side thereof an exterior friction reducing layer comprising casein and llO%, based on the dry weight of the casein, of a compound having the following formula:

N-CHQCHzC O OM wherein R is an aliphatic hydrocarbon group of from 10 to 1'8 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 18 carbon atoms and CH CI-I COOM, and M is selected from the group consisting of hydrogen and a cation.

2. A photographic element comprising a paper support having on one side thereof an exterior friction reducing layer comprising casein and llO%, based on the dry weight of the casein, of a compound having the following formula:

wherein R is an aliphatic hydrocarbon group of from 10 to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 18 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

3. A photographic element comprising an opaque paper support having on one side thereof an exterior friction reducing layer comprising casein and llO%, based on the dry weight of the casein, of a compound having the following formula:

wherein R is an aliphatic hydrocarbon group of from 10 to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 18 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

4. A photographic element comprising a paper support having a photosensitive layer on one side thereof and on the opposite side an opaque coating and an exterior friction reducing layer thereover comprising casein and based on the dry weight of the casein, of a compound having the following formula:

wherein R is an aliphatic hydrocarbon group of from to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 18 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

5. A photographic element comprising a paper support having a polyethylene coating on one side and on the opposite side an exterior friction reducing layer comprising casein and 110%, based on the dry weight of the casein, of a compound having the following formula:

wherein R is an aliphatic hydrocarbon group of from 10 to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 18 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

6. A photographic support comprising a film base composed of a compound selected from the group consisting of cellulose acetate, cellulose acetate butyrate, polystyrene, polycarbonate, and polyethylene terephthalate, and an exterior friction reducing layer thereon comprising casein and 110%, based on the dry weight of the casein, of a compound having the following formula:

wherein R is an aliphatic hydrocarbon group of from 10 to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 118 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

7. A multicolor image transfer photographic element comprising a film support, a plurality of light sensitive coatings on one side of said support, and on the opposite side of said support an exterior friction reducing layer comprising casein and 110%, based on the dry weight of the casein, of a compound having the following formula:

wherein R is an aliphatic hydrocarbon group of from 10 to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 1 ,8 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

8. A photographic element comprising a support having on one surface thereof a colloidal dispersion containing physical development nuclei, and on the reverse side an exterior friction reducing layer comprising casein and 1-10%, based on the dry weight of the casein, of a compound having the following formula:

wherein R is an aliphatic hydrocarbon group of from 10 to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 18 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

9. In a photographic element adapted for use in an image transfer process, which element comprises a support having at least one silver halide emulsion coating on one side thereof, the improvement which comprises an exterior friction reducing layer on the opposite side of said support, which layer comprises casein and 110%, based on the dry weight of the casein, of a compound having the following formula:

N-CHgCHz O 0 0M wherein R is an aliphatic hydrocarbon group of from 10 to 18 carbon atoms, R is selected from the group consisting of hydrogen, an aliphatic hydrocarbon group of from 10 to 18 carbon atoms and CH CH COOM, and M is selected from the group consisting of hydrogen and a cation.

10. A photographic support having on one side thereof an exterior friction reducing layer comprising .25-.30 gram per square foot of casein and 45-55%, based on the dry weight of the casein, of the alkali metal salt of N-alkyl-fl-iminodipropionate, said alkyl ranging from 12-18 carbon atoms.

11. A photographic support having on one side thereof an exterior friction reducing layer comprising .25-.30 gram per square foot of casein and 45-55%, based on the dry weight of the casein, of the alkali metal salt of N- alky-l-B-iminodipropionate, said alkyl ranging from 12-18 carbon atoms, and 13% hardener, based on the dry weight of the casein.

12. A photographic support having on one side thereof an exterior friction reducing layer comprising .25-.30 gram per square foot of casein and 45-55%, based on the dry weight of the casein, of the alkali metal salt of N- alkyl-B-iminodipropionate, said alkyl ranging from 12-18 carbon atoms, and 1-3% matting agent, based on the dry weight of the casein.

References Cited by the Examiner UNITED STATES PATENTS 1,680,636 8/1928 Renwick 96i87 2,173,480 9/1939 Jung 9687 2,955,970 10/1960 Rice et a1. 154102 3,133,816 5/ 1964 Ben-Ezra 9694 NORMAN G. TORCHIN, Primary Examiner.

R. H. SMITH, Assistant Examiner. 

1. A PHOTOGRAPHIC SUPPORT HAVING ON ONE SIDE THEREOF AN EXTERIOR FRICTION REDUCING LAYER COMPRISING CASEIN AND 1-10%, BASED ON THE DRY WEIGHT OF THE CASEIN, OF A COMPOUND HAVING THE FOLLOWING FORMULA: 